THE FLORIDA STATE UNIVERSITY ARTS AND SCIENCES ...

(Firestone et al., 1980). Green et al. (2008), in a study of five aquifers in the United States
showed that a significant relationship exists between the Dissolved Oxygen (DO) levels
and the rates of denitrification. The cut-off value of DO for denitrification to occur in
their study is set at 0.06 mmol/l – O2. There are several studies that set a minimum
oxygen level, but there is no consensus to an agreed minimum value. It is however
reasonable to assume that, given all other conditions being in favor of denitrification it
will occur in conditions where the oxygen concentration is less than 2 mg/l – O2
(Aravena & Robertson , 1998; Smith & Duff , 1988; Puckett & Cowdrey, 2002).
In some settings it is still possible for denitrification to occur at higher value. McNellie,
as quoted in Anderson (1998) reports the occurrence of denitrification at DO levels as
high as 5.1 mg/L. High denitrification rates were obtained even at oxygen concentrations
as high as 5 mg/L (Martienssen & Schops, 1999).
While there is no consensus set for the cutoff mark of dissolved oxygen, literature seems
to support the theory that denitrification tends to be greater in regions of lowest oxygen
concentration (Rivett et al., 2008; Korom, 1992).
1.2.3. Nutrient and micro nutrient activity
Besides carbon and nitrogen, denitrifying bacteria also need other nutrients such as
phosphorous and sulfur. In addition micro-nutrients such as B, Cu, Fe, Mn, Mo, Zn and
Co are also needed for effective metabolism (Rivett et al., 2008; Hiscock et al., 1991).
Spector (1957) reported a required ratio of 100: 20: 5: 1 for C: N: P: S for denitrification
to occur. Most groundwater contains adequate concentrations of the necessary minerals to
support microbial growth (Champ et al., 1979; Salbu, 1995). The adequate availability of
nutrients and micronutrients can be further supported through literature that report
denitrification as either carbon limiting or nitrate limiting while there are comparatively
fewer studies to show that phosphorous or sulfur is a limiting factor (Lowrance, 1992).
1.2.4. Temperature
The optimum temperature for denitrification is between 25ºC and 35ºC (77ºF - 95ºF)
(Korom, 1992), but denitrification processes can occur in the temperature range of 2ºC –
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